Abstract: A tuned radio frequency amplifier includes signal amplification means having an input and an output and first and second pairs of varactor diodes, each pair having an inductor connected across the anodes and a common tuning voltage supplied to the common cathode. The inductor of the first varactor diode pair provides an input for a signal from an antenna; and the inductor across the second varactor diode pair provides an output for the amplified signal. Means are provided for connecting the input of the signal amplification means to the common cathode of the first varactor diode pair and the output of the signal amplification means to the common cathode of the second varactor diode pair, whereby the range of tuning voltage required for a specified range of tuned frequencies is smaller than if the input and output of the signal amplification means were connected across the anodes of the varactor diode pairs.

Abstract: A stereo noise reduction circuit is disclosed having circuitry responsive to the automatic gain control voltage generated within an FM stereo receiver for reducing the noise associated with low levels of the RF carrier. A first portion of the noise reduction circuit provides for out-of-phase noise cancellation when the automatic gain control voltage reaches a first level and a second portion provides for rolling-off the higher frequencies of the output audio signals when the automatic gain control voltage reaches a second level.

Abstract: A voltage variable capacitor tuned radio receiver having a circuit which delays operation of a portion of the radio receiver circuit which includes the automatic frequency control circuit after the radio receiver is first energized until the filter capacitor at the output of the tuning voltage generator has charged to a selected tuning voltage to prevent the automatic frequency control circuit from locking the radio receiver onto an undesired RF carrier frequency.